SAO PAULO - A Brazilian rancher's conviction for the murder of a U.S. nun in the Amazon could help discourage attacks on rain forest activists that for decades have largely gone unpunished, environmentalists and legal officials said Tuesday.

View full sizeAssociated Press, FileIn this Feb. 12, 2004 file photo, missionary sister Dorothy Stang, of Ohio, is seen before entering the Para's legislature in Belem, northern Brazil. A rancher accused of ordering the murder of Stang, a U.S. nun and Amazon defender,was found guilty and sentenced to 30 years in prison Monday April 12, 2010 in Belem, Brazil.

Vitalmiro Moura was sentenced to 30 years for ordering the killing of 73-year-old Dorothy Stang in 2005 because she blocked him and another rancher from taking over land the government gave to farmers.

Hundreds of activists have been killed in Brazil in the last 20 years — but only about 80 triggermen, usually paid by powerful ranchers with land claims at stake, were behind bars before Tuesday. Moura is the only so-called mastermind of one of the killings to join them, raising hopes that the climate of impunity in the Amazon is finally nearing an end.

"It's obviously a sign that the times of violence without consequence are ending," said Paulo Adario, director of Greenpeace's Amazon campaign. "Putting the man accused of a brutal killing in jail shows to those who fight to protect the Amazon and to the criminals that violence will not go unpunished."

Moura denied any involvement in the killing and said he didn't even know the victim. Alex Noronha, one of his court-appointed lawyers, said he believes Moura is innocent but called the ruling "the manifestation of the society's will." He added that Moura would have to hire an attorney if he wants to appeal.

The case against the wealthy rancher was seen as a test of Brazil's ability to strengthen the rule of law in the largely lawless Amazon, which is also plagued by illegal activities such as unauthorized logging, and the prosecutor and the judge involved called the outcome a victory for the legal system.

"The judiciary showed that it does not succumb to the interests of the powerful," prosecutor Edson Cardoso was quoted as saying by the state news service Agencia Brasil.

"The verdict and sentencing sent a clear message that the law will be applied to everyone independent of his socio-economic status," Judge Raimundo Moises Alves Flexa said.

However both the judge and the Greenpeace activist cautioned that more convictions in similar cases are necessary if activists are to be truly protected.

"It could be a first small step, but there is still a long way to go," Flexa said.

Jurors found Moura guilty late Monday after 15 hours of deliberations, sparking jubilant celebrations from family members of Stang, supporters and activists who had camped and prayed outside the court.

"Justice has been made," David Stang told reporters in Belem. "My sister would be very happy. She believed in the Brazilian judicial system."

A native of Dayton, Ohio, and a naturalized Brazilian citizen, Dorothy Stang worked for three decades to preserve the rain forest and defend poor settlers' land rights.

Nun Rebeca Spires, who has worked in Brazil for four decades and knew Stang for 35 years, called the ruling a milestone victory: Because there is an "endless supply" of gunmen available for hire in the Amazon, she said, the ranchers who hire them must be imprisoned if the violence is to stop.

"We've waited so long for this verdict. This conviction sends a strong message to the other masterminds that the impunity is ending," Spires said.

Moura was previously convicted of Stang's murder and then acquitted in an automatic retrial. That decision was overturned last year on a technicality, however.